01 -
Preheat the oven to 350°F (175°C) and line a baking sheet with parchment paper.
02 -
In a medium bowl, whisk together the all-purpose flour, baking soda, and salt until evenly blended. Set aside.
03 -
In a large mixing bowl, cream the softened unsalted butter with the packed brown sugar and granulated sugar for 2–3 minutes until light and fluffy.
04 -
Beat in the egg and vanilla extract to the butter-sugar mixture until fully incorporated.
05 -
Gradually add the dry ingredients to the wet mixture, mixing gently until just combined and no streaks of flour remain.
06 -
Carefully fold in the Rice Krispies cereal, semi-sweet chocolate chips, and mini marshmallows (if using) until uniformly distributed throughout the dough.
07 -
Spoon rounded tablespoons of dough onto the prepared baking sheet, spacing each portion at least 2 inches apart.
08 -
Transfer the baking sheet to the preheated oven and bake for 10–12 minutes, until edges are golden brown but centers remain slightly soft.
09 -
Allow cookies to cool on the baking sheet for 5 minutes before transferring to a wire rack to cool completely.